سلولهای زنده برای انجام بسیاری از وظایف خود به انتقال انرژی از منابع خارجی نیاز دارند. همه ارگانیسم‌ها باید از طریق فتوسنتز و تنفس سلولی این انرژی را از مولکول های آلی موجود درغذا بدست آورند. تنفس با استفاده از اکسیژن و تولید ATP، باعث شکستن این سوخت می‌شود. مواد زائد این نوع تنفس، دی اکسید کربن و آب، مواد اولیه فتوسنتز هستند. در این اسلاید، من سعی می کنم چگونگی برداشت سلول‌ها از انرژی ذخیره شده در مولکولهای آلی و استفاده از آن برای تولید ATP از طریق تنفس سلولی را توضیح دهم.
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Living cells require transfusions of energy from outside sources to perform their many tasks. All organism need to obtain this energy from organic molecules of food through photosynthesis and cellular respiration. Respiration breaks this fuel down, using oxygen and generating ATP. The waste products of this type of respiration, carbon dioxide and water, are the raw materials for photosynthesis. In this slide, I try to explain how cells harvest this energy stored in organic molecules and used it to generate ATP through cellular respiration.
2. Outlines
• Energy for life
• Catabolic pathways
• Production of ATP
• Redox reactions: Oxidation &
Reduction
• Cellular Respiration
• Glycolysis
• Citric acid cycle
• Oxidative phosphorylation
• Electron transport chain
• chemiosmosis
• Fermentation and Anaerobic
Respiration
• Alcohol fermentation
• Lactic acid fermentation
• Regulation of cellular respiration
3. Energy for life
• The energy ultimately comes from the sun.
• Photosynthesis generates oxygen, as well as
organic molecules
• The organic molecules are used by the
mitochondria of eukaryotes as fuel for
cellular respiration.
• Respiration breaks this fuel down, using
oxygen and generating ATP.
• The waste products of respiration, carbon
dioxide and water, are the raw materials for
photosynthesis.
4. Catabolic Pathways - Respiration
• Catabolic reaction:
• Fermentation: is a partial degradation of
sugars or other organic fuel that occurs
without the use of oxygen.
• Aerobic respiration: the most efficient
catabolic pathway in which oxygen is
consumed as a reactant along with the
organic fuel
• Cellular respiration: includes both aerobic
and anaerobic processes:
• Some prokaryotes use substances other
than oxygen as reactants in a similar
process that harvests chemical energy
without oxygen. (anaerobic respiration)
• Production of ATP in form of heat
5. Catabolic Pathways – Redox reactions
• In chemical reactions, the transfer of one
or more electrons (e-) from one reactant
to another is called Oxidation-Reduction
(Redox) Reactions.
• Oxidizing Agent
• Reductive Agent
• Oxidation of Organic Fuel Molecules During
Cellular Respiration
6. Catabolic Pathways – Redox reactions
• In oxidation reactions, each electron
travels with a proton—thus, as a
hydrogen atom.
• These hydrogen atoms are not
transferred directly to oxygen
• They are passed first to an electron
carrier, a coenzyme called
nicotinamide adenine dinucleotide
(NAD)
• Derivative of the vitamin niacin.
• A well suited as an electron carrier:
• It can cycle easily between its oxidized
form, NAD+, and its reduced form, NADH.
• As an electron acceptor, NAD+
functions as an oxidizing agent during
respiration.
7. Catabolic Pathways – Redox reactions
• An electron transport chain consists of a
number of molecules, mostly proteins,
built into the inner membrane of the
mitochondria of eukaryotic cells (and the
plasma membrane of respiring
prokaryotes).
• Electrons removed from glucose are
shuttled by NADH to the “top,” higher-
energy end of the chain. At the
“bottom,” lower-energy end, O2 captures
these electrons along with hydrogen
nuclei (H+), forming water.
• Anaerobically respiring prokaryotes
have an electron acceptor at the end of
the chain that is different from O2.
8. Catabolic Pathways – Cellular Respiration
• Glycolysis, which occurs in the cytosol,
begins the degradation process by
breaking glucose into two molecules of a
compound called pyruvate.
• In eukaryotes, pyruvate enters the
mitochondrion and is oxidized to a
compound called acetyl CoA, which enters
the citric acid cycle. There, the breakdown
of glucose to carbon dioxide is completed.
• In prokaryotes, these processes take place
in the cytosol
• The enzyme dehydrogenase transfers
electrons from substrates to NAD+ or the
related electron carrier FAD, forming
NADH or FADH2.
The stages of cellular respiration
9. Catabolic Pathways –
Cellular Respiration
• Oxidative phosphorylation is the
mode of ATP synthesis in a
mitochondrion
• In eukaryotic cells, the inner
membrane of the mitochondrion is
the site of electron transport and
another process called chemiosmosis,
together making up oxidative
phosphorylation.
• Substrate-level phosphorylation is
another mode of ATP synthesis in a
mitochondrion when an enzyme
transfers a phosphate group from
substrate molecule to ADP
• Unlike oxidative phosphorylation an
organic phosphate is added to the ADP
13. Catabolic Pathways
Citric acid cycle
• To calculate on a per-glucose basis,
multiply by 2, because each glucose
molecule is split during glycolysis into
two pyruvate molecules.
15. Catabolic Pathways
Oxidative Phosphorylation
• Glycolysis and the citric acid cycle, produce
only 4 ATP molecules per glucose molecule,
all by substrate-level phosphorylation:
• 2 net ATP from glycolysis
• 2 ATP from the citric acid cycle.
• The electron transport chain is a collection of
molecules embedded in the inner membrane
of the mitochondrion in eukaryotic cells.
• The folding of the inner membrane to form
cristae increases its surface area, providing
space for thousands of copies of each
component of the electron transport chain
in a mitochondrion.
16. Catabolic Pathways
Oxidative Phosphorylation
• ATP synthase, the enzyme that makes ATP
from ADP and inorganic phosphate.
• Many copies of the protein complex have
populated the inner membrane of the
mitochondrion or the prokaryotic plasma
membrane
• Its first activity is hydrolyzing ATP to pump
protons against their concentration gradient.
• And the second activity is to use the energy of
an existing ion gradient to power ATP
synthesis.
• The process, in which energy stored in the
form of a hydrogen ion gradient across a
membrane is used to drive cellular work such
as the synthesis of ATP, is called
chemiosmosis.
• Chemiosmosis refers to the flow of H+
across a membrane unlike H2O in osmosis.
19. Catabolic Pathways
Fermentation and Anaerobic Respiration
• In the absence of oxygen, many cells use
fermentation to produce ATP by
substrate-level phosphorylation. NAD+ is
regenerated for use in glycolysis when
pyruvate, the end product of glycolysis,
serves as an electron acceptor for
oxidizing NADH.
• Two types of fermentation are:
• Alcohol fermentation
• Lactic acid fermentation
20. Catabolic Pathways
Fermentation and Anaerobic Respiration
• In alcohol fermentation, pyruvate is
converted to ethanol (ethyl alcohol) in
two steps:
• The first step releases carbon dioxide
from the pyruvate, which is converted to
the two-carbon compound acetaldehyde.
• In the second step, acetaldehyde is
reduced by NADH to ethanol. This
regenerates the supply of NAD+ needed
for the continuation of glycolysis.
• Many bacteria carry out alcohol
fermentation under anaerobic conditions.
Yeast (a fungus), in addition to aerobic
respiration, also carries out alcohol
fermentation.
21. Catabolic Pathways
Fermentation and Anaerobic Respiration
• During lactic acid fermentation, pyruvate
is reduced directly by NADH to form
lactate as an end product, regenerating
NAD+ with no release of CO2.
• Lactic acid fermentation by certain fungi
and bacteria is used in the dairy industry
to make cheese and yogurt.
22. Catabolic Pathways
The Catabolism of Other Molecules
• Carbohydrates, fats, and proteins can all
be used as fuel for cellular respiration.
• Monomers of these molecules enter
glycolysis or the citric acid cycle at various
points.
• Glycolysis and the citric acid cycle are
catabolic funnels through which electrons
from all kinds of organic molecules flow
on their exergonic fall to oxygen.
23. Catabolic Pathways
Regulation of Cellular Respiration
• Allosteric enzymes at certain points in the
respiratory pathway respond to inhibitors
and activators that help set the pace of
glycolysis and the citric acid cycle.
• Phosphofructokinase, which catalyzes an
early step in glycolysis, is one such
enzyme.
• It is stimulated by AMP (derived from
ADP) but is inhibited by ATP and by
citrate.
• This feedback regulation adjusts the rate
of respiration as the cell’s catabolic and
anabolic demands change.
24. Summary
• Energy for life
• Catabolic pathways
• Production of ATP
• Redox reactions: Oxidation &
Reduction
• Cellular Respiration
• Glycolysis
• Citric acid cycle
• Oxidative phosphorylation
• Electron transport chain
• chemiosmosis
• Fermentation and Anaerobic
Respiration
• Alcohol fermentation
• Lactic acid fermentation
• Regulation of cellular respiration
